In recent years, information terminal devices (hereinafter referred to as portable terminal devices) such as cellular phones, and Personal Digital Assistants (PDAs), which can be easily carried with, are widely available on the market. A portable terminal device includes a unit to pass information to a user visually using a small liquid crystal screen or the like, and a unit to pass information to a user aurally through a speaker, earphones, or the like. As a recording medium for such portable terminal devices, a universal memory card (e.g. IC card including SD Card™ and Memory Stick™), which includes nonvolatile memories such as a flash memory, has been widespread. Digital content, including video and audio, is stored into the memory card, and is viewed using a portable terminal device.
In Japan, terrestrial digital broadcast has made a full-fledged start, and content with high image quality has come to be digitally distributed. The proliferation of apparatuses such as hard disk recorders and Digital Versatile Disk (DVD) recorders, with which digital signals can be directly recorded, has facilitated the distributed content to be recorded easily in digital signal format. Patent Reference 1 discloses a copyright protection method using a hard disk and a memory card. The method prevents the unauthorized use of content by encoding and recording content into a hard disk and storing a key required for decoding into an area in which the security of a memory card is ensured.
Following the digitalization of content, various mechanisms to protect the rights of copyright holders have been proposed. One of these mechanisms is a rule called “copy-once”. Under this rule, the recorded digital content is authorized to be copied only once, and additional copying is not authorized. For example, the digital broadcast signal, to which a copy-once identifier is added, is not authorized to be copied on another medium, when being recorded on a recorder such as a hard disk recorder, a DVD recorder or the like. In the case where content is recorded on another medium, original content must be deleted. Provided that content is deleted, the recording of content onto another medium is called “move”.
Since the main application of stationary recorders such as hard disk recorders and DVD recorders is to be installed for home-use, content is required to be recorded and reproduced in high image quality as well as in high sound quality. Thus, storage devices with large storage capacity such as a hard disk and a DVD are used in the stationary recorders. A format capable of processing content in high image quality as well as in high sound quality is adopted for such content. The bit rate for such content is generally high.
On the other hand, it is assumed that portable terminal devices are carried with when being used, and reproduce content stored in a recording media such as a memory card or the like. Thus, a portable terminal device is required to display content on a relatively small display device, to be powered by a battery, and to be implemented with low power consumption. Thus, as a format for content to be recorded onto a portable terminal device, a format with a low-image quality and/or a low-sound quality is adopted. In other words, the bit rate of content is generally low.
Under the copy-once rule for example, when content of digital TV broadcast and the like is recorded, up to two pieces of such content can be stored in different recording media simultaneously. By utilizing the copy-once rule, content can be stored into a hard disk drive (HDD), a DVD and the like, having large-capacity as well as high-accuracy, and simultaneously into a memory card having small-capacity and low-accuracy.    Patent Reference 1: Japanese Open-Laid Patent Application No. 2002-368732